なお、vagrant は bundle 環境下で実行すると、次のようなメッセージが表示されますので、vagrant を普通に使うときには公式サイトからパッケージをダウンロードして使いましょう。
You appear to be running Vagrant in a Bundler environment. Because
Vagrant should be run within installers (outside of Bundler), Vagrant
will assume that you're developing plugins and will change its behavior
in certain ways to better assist plugin development.

/Users/.../bin/ruby extconf.rb --with-mysql-config=/usr/lo
cal/mysql/bin/mysql_config
checking for mysql_ssl_set()... no
checking for rb_str_set_len()... no
checking for rb_thread_start_timer()... no
checking for mysql.h... no
checking for mysql/mysql.h... no
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers. Check the mkmf.log file for more
details. You may need configuration options.